The present invention relates to a motor in which current supplied to plural-phase winding loads is electronically altered by means of plural transistors.
In recent years, as driving motors for OA appliances or AV apparatuses, motors in which a current path is electronically altered by means of plural transistors have been widely used.
FIG. 23 shows a motor of the prior art, and the operation of the motor will be briefly described. A rotor 501 has a field part configured by permanent magnets. In response to the rotation of the rotor 501, a position detection part 505 produces two sets of three-phase voltage signals L1, L2, and L3, and L4, L5, and L6. A first distributing unit 506 produces three-phase negative-side conduction control signals UL1, UL2, and UL3 responding with the voltage signals L1, L2, and L3, respectively, and controls the conduction of negative-side NPN-type power transistors 508, 509, and 510. A second distributing unit 507 produces three-phase positive-side conduction control signals UH1, UH2, and UH3 responding with the voltage signals L4, L5, and L6, respectively, and controls the conduction of positive side PNP-type power transistors 511, 512, and 513. According to this configuration, the current paths to three-phase windings 502, 503, and 504 is controlled.
However, the above-mentioned prior art configuration has the following problems.
In the prior art configuration, in order to reduce vibration of the motor, the NPN-type power transistors 508, 509, and 510 and the PNP-type power transistors 511, 512, and 513 supplied smooth drive currents to the windings 502, 503, and 504 by analoguely controlling the voltages between the emitter and the collector. However, the residual voltage of each power transistor was so large that a great power loss and heat generation were formed as a product of the residual voltage and the drive currents to the windings. As a means to solve this problem, a step-down chopper circuit is provided on the positive terminal side of a DC power source 530 so as to vary output voltages in accordance with the magnitudes of the drive currents to the windings 502, 503, and 504. However, as long as the power transistors were controlled analoguely, the residual voltages of the power transistors were large, which set limits to a reduction in the power loss. As another method of reducing the power loss, a switching control method can be performed to make the power transistors switching operations. However, there is no prior art that can easily smooth the drive currents to the windings 502, 503, and 504; the realization of the smooth drive currents required providing a large-scale circuit, which had a problem of boosting the cost.